Rewrite with only sin x and cos x.
sin 3x
a)2 sin x cos2x + cos x
b)2 sin x cos2x + sin3x
c)sin x cos2x - sin3x + cos3x
d)2 cos2x sin x + sin x - 2 sin3x

Question

Rewrite with only sin x and cos x. 
sin 3x 
a)2 sin x cos2x + cos x 
 b)2 sin x cos2x + sin3x 
 c)sin x cos2x - sin3x + cos3x 
d)2 cos2x sin x + sin x - 2 sin3x

amoodarya · Answer

sin(3x)=sin(x+2x)
=sinx cos 2x + cos x sin 2x
=sinx (2cos^2x -1)_cosx (2sinx cos x)

anonymous · Answer

so its c?

amoodarya · Answer

whats the original question?

anonymous · Answer

the original question is Rewrite with only sin x and cos x. 
sin 3x

amoodarya · Answer

ok 
you mean write sin3x by only (sinx , cos x) ?

anonymous · Answer

yes

amoodarya · Answer

then whats mean a,b,c,d 
because they use sin 2x
 or sin3x ?

anonymous · Answer

thos are the answer choice

amoodarya · Answer

c is not correct because 
if you put x=0 at sin3x=0 
c(0)=1
a(0)=1

anonymous · Answer

oh ok so what is it?

amoodarya · Answer

let f(x)=sin 3x
answer is equal to f(x)
ok 
so 
for example f(0)=0
or f(pi/2)=sin(3pi/2)=-1
if you put pi/2 in them only (d) is answer

amoodarya · Answer

understand ?

anonymous · Answer

yes thankyou!

amoodarya · Answer

i think that ques. has a logic problem 
i was teaching trigonometry for many years